Method of operating a rotor of a blood pump

ABSTRACT

A device for pumping blood, includes a housing having a distal end adapted to be coupled to a catheter, a proximal end having an outlet, and a tubular body extending between the distal and proximal ends along an axis. A rotor is rotatably disposed within the housing. A first magnetic bearing is operative to levitate the rotor along the axis within the housing. A second magnetic bearing controls a rotational frequency of the rotor. A third magnetic bearing controls a radial position of the rotor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 14/510,449,filed Oct. 9, 2014 (pending) which is a divisional of application Ser.No. 13/827,645, filed Mar. 14, 2013 (now U.S. Pat. No. 8,882,477), thedisclosures of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates generally to blood pumps and, morespecifically, to blood pumps having magnetically levitated and drivenrotors.

BACKGROUND

The human heart is the muscle that is responsible for pumping bloodthroughout the vascular network. Veins are vessels that carry bloodtoward the heart while arteries carry blood away from the heart. Thehuman heart consists of two atrial chambers and two ventricularchambers. Atrial chambers receive blood from the body and theventricular chambers, which include larger muscular walls, pump bloodfrom the heart. A septum separates the left and the right sides of theheart. Movement of the blood is as follows: blood enters the rightatrium from either the superior or inferior vena cava and moves into theright ventricle. From the right ventricle, blood is pumped to the lungsvia pulmonary arteries to become oxygenated. Once the blood has beenoxygenated, the blood returns to the heart by entering the left atrium,via the pulmonary veins, and into the left ventricle. Finally, the bloodis pumped from the left ventricle into the aorta and the vascularnetwork.

For the vast majority of the population, the events associated with themovement of blood happen without circumstance. However, for many peoplethe heart fails to provide adequate pumping capabilities. These heartfailures may include congestive heart failure (commonly referred to asheart disease), which is a condition that results in any structural orfunctional cardiac disorder that impairs the ability of the heart tofill with or pump blood throughout the body. Presently, there is noknown cure for heart disease and long-term treatment is limited to aheart transplant. With only a little over 2,000 patients receiving aheart transplant each year, and over 16,600 more on the waiting list fora heart, there is a persisting need for a cure or at the minimum a meansof improving the quality of life of those patients on the waiting list.

One such means of bridging the time gap while awaiting a transplant is acirculatory assist system. Circulatory assist systems may also beutilized as a destination therapy for individuals not eligible for aheart transplant. These systems, originally envisioned over thirty yearsago, provide assistance to the heart by way of a mechanical pump. Inthis way, blood is circulated throughout the vascular network despitethe diseased heart tissue. Traditionally, these circulatory assistsystems include an implantable or extracorporeal pump, a controller(internal or external), and inflow and outflow tubes connecting the pumpto the heart and the vascular network. Food and Drug Administration(FDA) approved circulatory assist systems can partially relieve symptomsof breathlessness and fatigue associated with severe heart failure anddrastically improve quality of life.

The wait time for receiving a heart transplant may be substantial.Therefore, circulatory assist systems, and particular the pumps drivingthem, must be designed for longevity. Furthermore, it is desirable toprovide an ideal and advantageous flow of blood therethrough withoutdamaging the blood. There is therefore a need in the art for a pump anda circulatory assist system which experiences low amounts ofinter-component friction during operation and causes less damage toblood than other pumps known in the art.

SUMMARY

In one embodiment, a device for pumping blood is provided and comprisesa housing having a distal end adapted to be coupled to a catheter, aproximal end having an outlet, and a tubular body extending between saidfirst distal and proximal ends along an axis. The device furthercomprises a rotor rotatably disposed within the housing, a firstmagnetic bearing operative to levitate the rotor along the axis withinthe housing, and a second magnetic bearing controlling a radial positionof the rotor, and a third magnetic bearing controlling a radial positionof the rotor.

In another embodiment, a device for pumping blood is provide andcomprises a housing having a distal end adapted to be coupled to acatheter, a proximal end having an outlet, and a tubular body extendingbetween the distal and proximal ends along an axis. The device furthercomprises a rotor rotatably disposed within the housing and a firstmagnetic bearing further comprising first and second permanent magnetsand operative to levitate the rotor to an axial position within thehousing. A second magnetic bearing is included and further comprises aplurality of vertically arranged pairs of electromagnetic coils and apole structure coupled to the rotor. The second magnetic bearing isconfigured to change or maintain a rotational frequency of the rotor. Athird magnetic bearing is provided and further comprises the pluralityof vertically arranged pairs of electromagnetic coils and the firstpermanent magnet. The third magnetic bearing is configured to change ormaintain a radial position of the rotor. The device further comprises aHall Effect sensor sensing the radial position and rotational frequencyof the rotor and a controller operably coupled to the Hall effect sensorand configured to communicate with the coils to change or maintain theradial position and rotational frequency of the rotor.

A method of operating a rotor of a blood pump is provided and compriseslevitating the rotor within a tubular body of the blood pump using afirst magnetic bearing, rotating the rotor about an axis within thetubular body using a second magnetic bearing, and maintaining the radialposition of the rotor relative to the axis using the third magneticbearing.

An alternative method of operating a rotor of a blood pump is providedand comprises levitating the rotor within a tubular body of the bloodpump using a first magnetic bearing, the first magnetic bearingcomprising a first permanent magnet and a second permanent magnet, thesecond permanent magnet operatively coupled with the rotor. The methodfurther comprises commencing rotation of the rotor within the tubularbody using a second magnetic bearing. The second magnetic bearingfurther comprises a plurality of vertically arranged pairs of coilscircumferentially disposed around the housing and a pole structurecoupled to the rotor. A current is sent to at least one of the pairs thecoils, thereby magnetizing the coil in a first pole direction and urgingan oppositely magnetized portion of the pole structure towards the coil.The method further comprises sensing a rotational frequency and a radialposition of the rotor. When a sensed rotational frequency is below athreshold level, the method further comprises sending a current to atleast a portion of the pairs of coils, thereby further rotating therotor. When the radial position of the rotor deviates from a thresholdposition about the axis, sending a current to a pair of coils, therebyurging the rotor towards the axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an exemplary method of accessing acavity of the heart.

FIG. 2 is a side view in partial cross-section of one embodiment of ablood pump as described herein.

FIG. 3 is a diagram of magnetic fields associated with the pump of FIG.2.

FIG. 4 is a side view of the pump of FIG. 2 including supplementaryelectromagnetic coils.

FIG. 5 is a side cross-sectional view of the pump of FIG. 2.

FIGS. 6A through 6C are top views of a schematic representation of thedevice of claim 1 showing the functionality of the coils.

FIG. 7 is a top view of a schematic representation of an alternativeembodiment of a device as described herein.

FIG. 8 is a schematic diagram of the controllers, sensors and circuitryof the pump of FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning now to the figures, and in particular to FIG. 1, an implantedcirculatory assist system 10 is shown within a chest cavity of a patient14 with the heart 12 shown in cross-section. For illustrative purposes,certain anatomy is shown, including a right atrium 16, a left atrium 18,a right ventricle 20, and a left ventricle 22. Blood from the left andright subclavian veins 24, 26 and the left and right jugular veins 28,30 enters the right atrium 16 through the superior vena cava 32 whileblood from the lower parts of the body enters the right atrium 16through the inferior vena cava 34. The blood is pumped from the rightatrium 16, to the right ventricle 20, and to the lungs (not shown) to beoxygenated. Blood returning from the lungs enters the left atrium 18 viapulmonary veins and is then pumped into the left ventricle 22. Bloodleaving the left ventricle 22 enters the aorta 38 and flows into theleft subclavian artery 40, the left common carotid 42, and thebrachiocephalic trunk 44 including the right subclavian artery 46 andthe right common carotid 48.

With respect to the implanted circulatory assist system 10, two cannulaeextend between the vascular network and a pump 50, which may be anyimplantable or extracorporeal pump that may be radially- and/oraxially-driven. Those skilled in this art, however, recognize that othertypes of pumps may be used in other embodiments but may include pumpssuch as those described in U.S. patent application Ser. No. 11/627,444,published as 2007/0197854, which is incorporated herein by reference inits entirety.

FIG. 2 illustrates the pump 50 in cross-section. In particular the pump50 includes an elongate pump housing 52 having a first end 53 coupled toa transition portion of the catheter (shown in hidden lines) and atubular body 56 extending from the first end 53 along a longitudinalaxis 58 of the pump housing 52. The first end 53 may be secured to thetransition portion by rigid barbs 60, adhesive, or any other couplingtechnique. In one embodiment of the present invention, the tubular body56 is defined by a pump inlet 62 at the first end 53 and a pump outlet64 at the second end 55. There is a shroud 81 (FIG. 5) encasing at leasta portion of the housing 52 and the magnetic components, as disclosedbelow. Blood flows in the inlet 62 at the first end 53 in the directionof arrows 57 and out of the outlet 64 at second end 55.

Various components of a blood pump 50 are housed within the pump housing52 to draw blood from the catheter 54 into the tubular body 56. Forexample, the blood pump 50 may comprise an impeller 66 and associatedimpeller blades 68 positioned within the tubular body 56. It will beappreciated that the impeller 66 is only schematically illustrated andmay take many forms, including a form as generally shown herein. Thepump 50 may further include a support pin 70 to maintain the axialposition therein of the impeller 66 prior to levitation. Notably, asdisclosed herein, “impeller” and “rotor” are used interchangeably andare meant to refer to reference number 66.

The impeller 66 further includes a rotor magnet 74 having dimensionssuitable such that the impeller 66 may reside and rotate freely withinthe tubular body 56. The rotor magnet 74 is a dipole configured to belevitated within the tubular body 56. In one exemplary embodiment of thepresent invention, the rotor magnet 74 may be 6 mm in diameter and 3 mmin height for pumps configured to operate as left ventricular assistpumps; yet, it would be readily appreciated that the size of the rotormagnet 74 may vary and depend, at least in part, on the size of theimpeller blades 68 and a desired blood flow rate. The impeller blades 68are configured to prevent damage to the blood traveling through thetubular body 52.

In one embodiment, the levitation of the impeller 66 is accomplished dueto a first magnetic bearing. More specifically, the first magneticbearing includes the ring magnet 76 and the rotor magnet 74 which, inone embodiment, are both permanent magnets. The ring magnet 76 and therotor magnet 74 are configured such that the oppositely magnetized sidesare facing one another. For example, the north pole side 78 a of therotor magnet 74 faces the south pole side 80 a of the ring magnet 76.Moreover, the configuration of the magnets 74, 76 may be chosen suchthat the interaction between the magnets 74, 76 creates an asymmetricalpotential energy well, as shown by the magnetic field diagram in FIG. 3.The radial potential is shown in the FIG. 3 as a generally hemisphericalshape 73. The asymmetric potential well is created due to the presenceof ring magnet 76 opposing only one side the rotor magnet 74. Thepotential well creates stability in the axial direction. Because thedepth of the well correlates with the amount of instability in theradial direction, the well may be designed in order to provide the leastradial instability while also providing a proper amount of axialstability. In one embodiment, the rotor magnet 74 includes a 6 mmdiameter and a 3 mm height. The ring magnet 76 includes an innerdiameter of 8 mm, an outer diameter of 14 mm and a height of 3 mm. Thepotential well creates interactions between the respective magneticfields of each magnet 74, 76, which results in levitation of the rotormagnet 74 relative to the ring magnet 76. Moreover, the asymmetricpotential well may be configured to provide a levitation forceapproximately equal and opposite to the fluid forces resulting from theblood flow and pumping action (i.e., rotation of the impeller 66). Thisprovides several benefits, including simplification of design. In orderto vary the levitation force and the size of the asymmetric potentialwell, the relative sizes of the rotor and ring magnets 74, 76 may bealtered.

Therefore, while the impeller 66 may be levitated by the potential well(FIG. 3), the rotor magnet 74 and thus the impeller 66 may inherently beunstable in the radial direction unless the rotor magnet 74 is rotating.Even then, the rotor magnet 74 may be unstable such that the rotormagnet 74, and thus the impeller 66, may tilt or move radially away fromaxis 58. The rotation of the rotor magnet 74 is operative to providestability in the radial direction of the rotor magnet 74 and thus theimpeller 66. The rotation of rotor magnet 74 is effectuated at least inpart by a second magnetic bearing, which is discussed in more detailbelow. The embodiment shown in FIGS. 2, 4 and 5 shows the ring magnet 76being situated distally relative to the rotor magnet 74. However, inother embodiments, it may be appreciated that the ring magnet 74 may besituated proximally relative to the rotor magnet 74 and still providethe potential well that is operative to levitate the rotor magnet 74,and thus the impeller 66, within the tubular body 56.

Alternatively, the levitation of the impeller 66 may be accomplished byuse of alternative materials, such as diamagnets. As understood by aperson skilled in the art, diamagnets are non-ferrous materials thatwhen placed in a magnetic field, exhibit a repulsion force towards themagnetic source. Therefore, in a preferred embodiment, at least one ofthe rotor magnet 74 or the ring magnet 76 may comprise a diamagnet.Preferably, in that embodiment, the rotor magnet 74 is a diamagnet whilethe ring magnet 76 is a permanent magnet as disclosed herein.

The magnetic portion or pole structure 72 may further include two ormore poles on both top and bottom edges 82, 84 of the rotor magnet 74.In one embodiment, the top and bottom edges 82, 84 each include a fourpole structure 72, which may be constructed by magnetic coding of theedges of the rotor magnet 74 by methods such as those taught in U.S.Pat. No. 7,800,471, issued on Sep. 21, 2010, and entitled FIELD EMISSIONSYSTEM AND METHOD, such magnetic coding services commercially-availablefrom Correlated Magnetics Research, LLC (New Hope, Ala.). Alternatively,as shown in FIGS. 5 and 6A-C, the structure may include physicallyembedded miniature sub-magnets, or pill magnets 88 a, 88 b within theimpeller 66. In any event, the pole structure is positioned such thatthe resultant magnetic field is oriented to oppose the magnetic field ofthe rotor magnet 74 or radially outwardly from the rotor magnet 74. Thepole structure 72 may be provided to function as one part of a magneticbearing that interact with the coils 92 as described herein. The polestructure 72 may alternatively include a magnet including several poles,such as a quadropole magnet, which may then be attached or coupled tothe rotor magnet such that it is also embedded in the impeller 66.

One embodiment of the pole structure 72 is shown in FIGS. 5 and 6A-C. Inthe embodiment shown in FIGS. 5 and 6A-C, there are four sub-magnets, orpill magnets 88 a, 88 b on the top and the bottom 82, 84 of the rotormagnet 74, respectively. In alternative embodiments, however, there maybe more pill magnets 88 a, 88 b on each of the top and the bottom 82, 84such as six or eight. Alternatively, there may be less, such as two.Preferably, as shown in FIG. 5, the pill magnets 88 a, 88 b are embeddedin the impeller 66. The pill magnets 88 a, 88 b are preferablycylindrically shaped and axially magnetized (FIGS. 6A-C). In anotherembodiment, the pill magnets 88 a, 88 b may be diametrically magnetized.In yet another embodiment, the pill magnets may be a shape other than acylinder, such as a triangular or rectangular prism, or another shape.The pill magnets 88 a, 88 b may be situated such that the direction ofmagnetization 87 of the pill magnets 88 a, 88 b is tangent to thedirection 91 of rotation of the impeller 66. However, depending on theshape and configuration, the direction of magnetization 87 of the pillmagnets 88 a, 88 b may be different.

The pump 50 further includes a plurality of electromagnetic coils 92 a,92 b disposed on or adjacent the housing 52. In a preferred embodiment,as shown in FIGS. 2, 4 and 5, the pump 50 includes four verticallyarranged, equally circumferentially spaced pairs of electromagneticcoils 92 a, 92 b. Each pair of coils 92 a, 92 b includes upper and lowercoils 92 a, 92 b, respectively. Each vertically arranged pair of coils92 a, 92 b is in series and counterwound such that, for example, uppercoil 92 a of a pair is wound in a counterclockwise direction and thelower coil 92 b is wound in a clockwise direction. However, in analternative embodiment, the coils may be wound in alternativeconfigurations. For example, coils 92 a, 92 b could also be wound thesame direction and wired so that the current flows in one directionthrough the top and the opposite direction in the bottom, therebyproducing opposite magnetic fields. The coils 92 a, 92 b are preferablyencased with housings 93 comprising a non-magnetic material as not tointerfere with the functionality of the pump 50. In an alternativeembodiment, however, there may be less than four vertically arrangedpairs of coils 92 a, 92 b. For example, there may be more than fourpairs, or less than four pairs. There may be supplemental coils 94, asshown in FIG. 4.

In one embodiment, the coils 92 a, 92 b may comprise an iron core (notshown) to strengthen the magnetic field emitted by the coils 92 a, 92 b.The coils 92 a, 92 b and the pole structure 72, such as the pill magnets88 a, 88 b, may be the second magnetic bearing that effectuates therotation of the rotor magnet 74, and thus the impeller 66. The rotationof the rotor magnet 74 and impeller 66 provides for axial stability ofthe levitated rotor magnet 74, and thus the impeller 66. The rotation-ofthe rotor magnet 74 and thus the impeller 66 are described in moredetail below. The device further includes a third magnetic bearing whichis configured to control a radial position of the rotor 66. As describedin further detail below, the third magnetic bearing includes the rotormagnet 74 and the coils 92, 92 b.

Preferably, the coils 92 a, 92 b are wound from a material, such ascopper, capable of conducting electricity such that a current willtravel through the coils 92 a, 92 b and energize the coils 92 a, 92 b,thereby magnetizing the coils 92 a, 92 b. Coils 92 a, 92 b receivingcurrent and thereby being magnetized may be referred to herein as“energized” or “magnetized.” The direction of the current flow throughthe coils 92 a, 92 b determines the direction of magnetization, i.e.,whether the coils will be magnetized as a south pole or a north pole.For example, in a preferred embodiment, the upper coils 92 a of a pairare wound in the clockwise direction such that when the upper coils 92 aare energized, the upper coils 92 a are magnetized in the north poledirection, as indicated by “N” on FIG. 6A-C. Similarly, in a preferredembodiment, the lower coils 92 b are wound in the counterclockwisedirection such that when the lower coil 92 b is energized, the lowercoils 92 b are magnetized in the south pole direction (not shown).

Because each vertically arranged pair of coils 92 a, 92 b in a preferredembodiment are in series, when the coils 92 a, 92 b are energized whenreceiving a current, the upper coils 92 a are magnetized in the northpole direction and the lower coils 92 b are magnetized in the south poledirection. However, as will be recognized by persons skilled in the art,the current may be sent in different directions to the upper and lowercoils 92 a, 92 b, resulting in different magnetization directions ofeach pair of coils 92 a, 92 b. Ultimately, changing the direction of thecurrent directed into the coils 92 a, 92 b changes whether a coil 92 a,92 b is magnetized in the north or south pole direction.

In one embodiment, each coil 92 a, 92 b comprises a #42 AWG copper wirewith approximately 750 turns per coil 92 a, 92 b, made by PrecisionEcowind, Inc. of North Fort Myers, Fla. With this diameter and amount ofturns, the resistance per coil 92 a, 92 b is approximately 50Ω. However,the coil 92 may comprise a different diameter, material, and amount ofturns, depending on the desired characteristics of the coils 92 a, 92 b,which ultimately depend on the desired characteristics of the blood pump50 (i.e., desired rotational frequency of the blood pump 50 or requiredforce to radially align the impeller 66). The current sent to the coils92 a, 92 b to thereby energize the coils 92 a, 92 b may be betweenapproximately 0 mA and 200 mA and depends on the characteristics of thecoils 92 a, 92 b described herein as well as the desired characteristicsof the blood pump 50.

FIGS. 6A through C show an embodiment of the pump 50 showing the uppercoils 92 a and upper pill magnets 88 a of the pump 50. A second magneticbearing is utilized in order to begin rotation of the impeller 66. Acurrent may be sent to diametrically opposed pairs of coils 92 a, 92 bsimultaneously by the controller (FIG. 8), thereby magnetizing the pairsof coils 92 a, 92 b in a certain direction. The magnetized coils 92 a,92 b then either attract or repel one or more of the pill magnets 88 a,88 b, depending on the rotational location of each of the pill magnets88 a, 88 b relative to the magnetized coils 92 a, 92 b. In order toclarify the functionality of the coils 92 a, 92 b during the operationof the device, the specific upper coils 92 a are labeled 1, 2, 3 and 4,while the specific upper pill magnets 88 a are labeled A, B, C, and D inFIG. 6A-C. Preferably, to begin rotation, coils 1 and 2 are energizedand are thereby magnetized in the north direction. The south poles ofpill magnets B, A thereby become attracted to, and are urged towards,coils 1 and 2, respectively. Because of the diametrically opposedconfiguration of the energized coils 1, 2, the attractive forces areessentially balanced. Furthermore, because the pill magnets B, A areembedded in the impeller 66, and the rotation of pill magnets B, Acauses the impeller 66 to begin to rotate in the clockwise direction 91.The interaction between the lower coils 92 b and lower pill magnets 88 bwould correspond to the interaction between the upper coils 92 a andupper pill magnets 92 a. For example, in a preferred embodiment asdisclosed above, the lower coils 92 b are magnetized in an opposite poledirection of the upper coils 92 a. Therefore, in order to attract orrepel the lower pill magnets 88 b as discussed herein, the configurationof the lower pill magnets 88 b may need to be reversed such that thenorth poles and south poles are facing opposite directions as shown inFIGS. 6A-C.

The Hall Effect sensors 96 sense the magnetic fields of the polestructure 72 (such as the pill magnets 88 a, 88 b) as well as the rotormagnet 74. With this magnetic field information, the Hall Effect sensors96 may sense the radial and axial positions of the pill magnets 88 a, 88b, as well as the rotational frequency of the pill magnets 88 a, 88 b,and thus the impeller 66. The Hall Effect sensors 96 essentiallydetermine whether the rotation frequency is at, below, or above athreshold rotational frequency. Further, the Hall Effect sensors 96communicate with the controller 98 (FIG. 8) to selectively energizecertain coils 92 a, 92 b to rotate the impeller 66. Preferably, the HallEffect sensors 96 use the rotational frequency and position informationto communicate with the controller 98 as to which coils 92 a, 92 b toenergize and/or de-energize. Using the upper pill magnets and coils 88a, 92 a by way of example, as a pill magnet 88 a approaches a coil 92 a,the controller 98 may de-energize the coil 92 a until the pill magnet 88a rotates past the coil 92 a. More specifically, in FIG. 6B, pillmagnets B, A have rotated past de-energized coils 3 and 4, respectively.The north poles of pill magnets B, A are facing the coils 3, 4,respectively. After the Hall Effect sensor 96 has sensed that the pillmagnets B, A have rotated past coils 3 and 4, the sensor 96 communicateswith the controller 98 regarding the position of pill magnets B and A.The controller 98 then energizes coils 3, 4 in the north direction andpill magnets B, A are repelled away from coils 3, 4. Because of thediametrically opposed configuration of the energized coils 3, 4, therepelling forces are essentially balanced and the impeller 66 continuesto rotate about the axis 58. The upper coils 92 a as shown in FIGS. 6A-Cmay be magnetized in the north direction. However, in alternativeembodiments, the selectively energized coils 3, 4 may be magnetized inthe south direction. Therefore, in that alternative embodiment, theconfiguration of the pill magnets B, A may need to be altered in orderfor the repelling and/or attractive forces to occur as coils 3, 4 areselectively energized. The orientation and configuration of the pillmagnets 88 a, 88 b relative to the coils 92 a, b may be determined bythe desired rotational direction.

Moreover, it may be appreciated that in embodiments with an alternativeconfiguration or different amount of coils 92 a, 92 b and/or pillmagnets 88 a, 88 b, for example, the rotational frequency may be alteredor maintained in similar manner such that the forces on the rotor 66 arebalanced, thus causing rotation of the rotor 66. For example, asdiscussed above, the embodiment as shown in FIGS. 6A-C includes fourvertically arranged pairs of coils 92 a, 92 b. One manner of maintainingor altering the rotation of the rotor 66 is, as discussed, sending acurrent to diametrically opposed pairs of coils 92 a, 92 b such that themagnetic forces from each coil 92 a, 92 b may be balanced along the axes100, 102 and thus rotation of the rotor 66 occurs. However, which coils92 a, 92 b to energize in order to provide balanced magnetic forces uponthe rotor or impeller 66 depends on the configuration and number of thecoils 92 a, 92 b as well as the configuration of the pole structure 72,such as the number of pill magnets 88 a, 88 b. In an alternativeembodiment, rather than including a pole structure 72, such as pillmagnets 88 a, 88 b, for rotation, the coils 92 a, 92 b may interact withthe dipole moment of the impeller magnet 74 in order to effect rotationof the rotor magnet 74, and thus the rotor 66.

The Hall Effect sensors 96 also use the magnetic field information ofthe pole structure 72 (such as the pill magnets 88 a, 88 b) and therotor magnet 74, to sense the radial position of the impeller 66,relative to the axis 58 of the pump 50. To control radial position ofthe rotor 66, a third magnetic bearing is utilized. In a similar manneras with respect to the rotational frequency discussed hereinabove, theHall Effect sensors 96 communicate with the controller 98 to selectivelyenergize certain coils 92 to alter the radial position of the rotormagnet 74, and thus the impeller 66, relative to the axis 58. Asdescribed herein, “off-axis” may be used to characterize the position ormovement of the impeller 66 where the impeller 66 is positioned radiallyaway from the axis 58 along axes 100 and 102, which are transverse tothe axis 58 of the blood pump 50. Moreover, axes 100, 102 are transverseto one another. Which coils 92 a, 92 b are energized depends on theoff-axis position of the impeller 66.

As shown in FIG. 6B, the radial position of the impeller 66 ischaracterized by an off-axis position along a single axis 100, or agenerally left direction, due to the radial instability caused by theasymmetric potential well (FIG. 3). The Hall Effect sensors 96 may sensethat the rotor 66 is not in a threshold position, the threshold positionbeing characterized by the center axis 67 of the rotor 66 beingessentially aligned with axis 58. Therefore, it may be desirable toalter the position of the impeller 66 in the generally right directionalong axis 100. To accomplish this positional alteration, the HallEffect sensors 96 communicate with the controller 98 to energize coil 4in the north direction, as indicated by arrows 97. Because each pair ofcoils 92 is wired in series and counterwound, the lower coil 92 b belowcoil 4 would be magnetized in the south direction. The rotor magnet 74,as discussed above, is oriented such that the north pole side 80 a isessentially adjacent the upper coils 92 a (i.e. coil 4), while the southpole side 80 b is essentially adjacent the lower coils. Thenorth-direction magnetization of coil 4 thereby repels the north poleside of 80 a, while the south-direction magnetization of the lower coil92 b associated with coil 4 repels the south pole side 80 b. Therefore,the forces from coil 4 and the associated lower coil 92 b are balancedangularly with respect to axis 58. Moreover, energizing the coilsgenerates forces that provide stability in the radial direction. Therotor magnet 74, and thus the impeller 66, are thereby urged towards theaxis 88 along axis 100. It may be appreciated that, instead ofenergizing coil 4 to repel rotor magnet 74 away from coil 4 and towardsaxis 58 along axis 100, coil 3 may be energized in a direction toattract rotor magnet 74 towards coil 3 (and the associated lower coil 92b), thereby urging the impeller 66 towards the axis 58. Moreover, whereextra force may be needed to urge the rotor 66 in the direction of axis58, coils 3 and 4 may be energized such that coil 3 attracts theimpeller towards axis 58 and coil 4 repels the impeller 66 towards axis58. It may be appreciated that, due to the generally hemispherical shapeof the potential well, the impeller magnet 74 may be urged slightly inthe axial direction during radial positioning by the coils 92 a, 92 b.

As shown in FIG. 6C, the radial position of the impeller 66 ischaracterized by a movement in the left and down directions along axes100 and 102, respectively, and radially away from the axis 58.Therefore, it may be desired to move the impeller 66 in the up and rightdirections towards the axis 58. To accomplish this positionalalteration, the Hall Effect sensors 96 communicate with the controller98 to energize adjacent coils 1 and 4 in the north pole direction, asindicated by arrows 97, and the associated lower coils (not shown) inthe south pole direction. Similar to the description of FIG. 6B above,magnetizing coils 1 and 4 and the associated lower coils (not shown)thereof urges the rotor magnet towards axis 58 due to the repellingforce between the energized coils and the rotor magnet 74.

Altering or maintaining the radial position of the rotor 66 as describedherein with respect to FIGS. 6B and 6C also assists in counteractingtilt of the rotor 66. The natural tendency of the south pole side 78 aof the rotor magnet 74 is to be attracted to the north pole side 80 a ofthe ring magnet 76. Therefore, as the rotor 66 rotates, the rotor 66 mayexperience tilt, wherein a center axis 67 of the rotor 66 is angularlydisplaced relative to the axis 58. The device and method ofcounteracting off-axis radial movement as described herein is alsoadapted to counteract tilt. In an alternative embodiment, it may beadvantageous to provide additional coils 92 a, 92 b for alterationand/or maintenance of rotational frequency, radial position and tilt. Inone embodiment, for example, the device may be configured to energizeone or more coils 92 from one of the upper or lower sets 92 a, 92 b inorder to urge the rotor 66 angularly towards the axis 58.

It is appreciated that the manners, frequency and continuity ofenergizing the coils 92 and the directions of magnetization resultingtherefrom may be altered depending on the number of and configurationsof the pill magnets 88 a, 88 b and coils 92 a, 92 b. The descriptionshereinabove of altering or maintaining the rotational frequencies andradial positions of the impeller 66, as well as counteracting tilt, aresimply examples and are not meant to limit the device and methoddescribed herein to only those examples.

One alternative embodiment is shown in FIG. 7. For example, where thereare more than four vertically arranged pairs of coils 92 a, 92 b, theamount of ways that the coils 92 a, 92 b may be energized to alter ormaintain the rotational frequency, radial position, and tilt isincreased. By way of example, in one embodiment, there may be eightpairs of vertically arranged coils 92 a, 92 b. This embodiment mayeffectuate the control of rotational frequency, radial position and tiltas described hereinabove. As in previously disclosed embodiments, whichcoils 92 a, 92 b are energized depends on the off-axis position of theimpeller or rotor 66. For example, as shown in FIG. 7, the impeller 66has moved off-axis in the downward direction along axis 102. Because ofthe additional coils, there is an increased amount of ways in which therotor 66 may be urged towards the axis 58. For example, depending on thepositions, and magnetization configuration of the rotor magnet 74, thecoils 2, 5 and 8 may be energized and attract, or essentially pull therotor magnet 74, thus urging the rotor in the direction of the axis 58along axis 102. Coils 1, 6 and 7 may be concurrently energized such thatit provides a magnetic force such that it repels, or pushes, theimpeller magnet 74. This repulsive force from coils 1, 6 and 7 maythereby balance the force from coils 2, 5 and 8 directing the rotoralong axis 102, thus maintaining the rotor rotating about axis 58. It isappreciated, as disclosed previously, that the lower coils (not shown)associated with coils 1, 2, 5, 6, 7 and 8 may be oppositely magnetizedand simultaneously energized with the associated upper coils 1, 2, 5, 6,7 and 8, thereby preferably balancing the magnetic forces from thecoils. Moreover, as previously discussed, the radial alteration andmaintenance of the rotor 66 by the coils 92 a, 92 b also assists incounteracting tilt of the rotor 66. FIGS. 6A-C and 7 are provided asexemplary embodiments. These figures and the disclosure regarding thesefigures are provided as an example of just a few manners in which therotational frequency, radial position and tilt may be altered ormaintained using the device as disclosed herein. It is appreciated thatthe amount of coils 92 a, 92 b, and the pole structure 72, such as theamount pill magnets 88 a, 88 b, may vary. Furthermore, the size,orientation, position and characteristics of the rotor magnet 74 may bevaried. Moreover, the manner in which the coils 92 a, 92 b arecontrolled in order to alter or maintain the rotational frequency,radial position and tilt may also vary. It is further appreciated thatwhen varying the amount of coils 92 and the pole structure 72,additional controllers 98 (FIG. 8) and Hall Effect sensors 96 may berequired.

Due to the loading on the impeller, it may also be appreciated bypersons skilled in the art that the flow of blood through the housing 52past the impeller, as well as the rotation of the impeller 66, may causethe impeller 66 to oscillate in the axial direction along axis 58. TheHall Effect sensors 96 are configured to detect the oscillation of theimpeller 66. One of the embodiments described herein may be configuredto counteract oscillation of the impeller 66. On the other hand,additional coils 92 a, 92 b may be provided in order to counteract theaxial oscillation of the impeller 66.

In another alternative embodiment, a blood pump 50 includes asupplemental set of coils 94 (shown in phantom in FIG. 4)circumferentially disposed about the housing 52. Preferably, thesupplemental coils 94 comprise four coils 94 equally circumferentiallyspaced, wherein each secondary coil 94 is offset ninety degrees fromadjacent pairs of vertically arranged coils 92. In the embodiment shownin FIG. 4, the vertically arranged pairs of coils 92 a, 92 b areutilized for maintaining or altering the radial position of the impeller66 in the same manner as substantially described herein. Thesupplemental coils 94 in this embodiment may be utilized for maintainingor altering the rotational frequency of the impeller 66 in the samemanner as described substantially herein. Because of the supplementalcoils, one or more additional Hall Effect sensors 96 may be required.Alternatively, the vertically arranged pairs of coils 92 a, 92 b may beutilized for maintaining or altering the rotational frequency of theimpeller 66, while the secondary coils 94 may be utilized formaintaining or altering the radial position of the impeller 66.

The rotational frequency of the pill magnets 88 a, 88 b, and thus theimpeller 66, are essentially continuously sensed or monitored by theHall Effect sensors 96. The Hall Effect sensors 96 essentiallycontinuously communicate with the controller 98 to energizediametrically opposed sets of coils 92 a, 92 b, depending on thepositions of the pill magnets 88 a, 88 b, in order to change therotational frequency of the impeller 66 or to maintain the rotationalfrequency of the impeller 66. The required rotational frequency of theimpeller 66 depends on certain variables such as the physiological needsof the patient and the dimensions of the impeller 66 and of the bloodpump 50, for example. In one embodiment of a blood pump 50 having aninner housing diameter of 5 mm, a rotational frequency of 17,000 to32,000 revolutions per minute produces a flow of 0.3 to 2.5 LPM atnormal physiological pressures as known to those skilled in the art. Theconfiguration of the blood pump of the aforementioned embodiment allowsthe blood pump 50 to be smaller than the blood pumps known in the art.The smaller size of blood pump 50 provides a less invasive configurationand can lower costs.

More specifically, there is a plurality of Hall Effect sensors 96circumferentially disposed on the device 50. Preferably, there are atleast two Hall Effect sensors 96 equally circumferentially disposed onthe device 50. As shown in FIGS. 2, 4 and 5, the device includes fourHall Effect sensors 96, where each Hall Effect sensor 96 is essentiallyaligned with a vertically arranged pair of coils 92 a, 92 b. Each HallEffect sensor 96 may be used to sense at least one of the rotationalfrequency and the radial position of the impeller 66. However, in oneembodiment, one or more of the Hall Effect sensors 96 may be used tosense only the rotational frequency and another portion of the HallEffect sensors 96 may be used to sense the radial position of theimpeller 66.

FIG. 8 shows a control loop 104. As disclosed herein, and with referenceto FIG. 8, the Hall Effect sensors 96 communicate with at least onecontroller 98 in order to selectively energize, or send current through,the coils 92. In a preferred embodiment, there is a plurality ofcontrollers 98 communicating with the sensors 96. More preferably, eachcontroller 98 is a proportional-integral-derivative (PID) controllerwhich, based on the information sent it from the Hall Effect sensors 96based on the magnetic field information, calculates the present, pastand future errors. To adjust for the present, past and anticipatedfuture errors (such as off-axis rotation), the PID controllers 96 thenselectively energize, or send a current through, one or more coils orpairs of coils 92 a, 92 b by way of the H-Bridge 106.

More specifically, the Hall Effect sensors 96 receive the magnetic fieldinformation from the rotor magnet 74 and the pole structure 72. With themagnetic field information from the Hall Effect Sensors, the controller96 is able to determine the position and rotational frequency of therotor magnet 74 and the pole structure 72, and thus the impeller 66, andcompare such with threshold data. The radial position may be sensed inthe X and Y positions (FIG. 8), such as along axes 100 and 102 (FIGS. 6Athrough 6C). The threshold data may also be obtained through observanceof the current traveling in the coils 92 a, 92 b. In at least oneembodiment, it is observed that as the impeller 66 approaches thethreshold position, the current passing through the coils reduces.Observing that phenomenon may allow a person skilled in the art todetect the position and rotational frequency of the impeller 166. Thethreshold data may include a predetermined, desired rotational frequencyand radial position. When the rotational frequency and radial positionas sensed by the Hall Effect sensors deviate from the predetermined,desired values, the controller sends a signal over the H-Bridge, therebyselectively energizing coils 92 a, 92 b.

The coils 92 a, 92 b which are energized depends on the desired outcomeas described above with respect to at least FIGS. 6A-C, such as alteringor maintaining the radial position or rotational frequency of theimpeller 66. In one embodiment, there are four PID controllers 98, eachbeing part of a control loop 104 including an H-bridge 106. However, thenumber of, type, and arrangement of the controllers 98 as describedherein is but one possibility of controlling the device 50 as describedherein and the disclosure is not meant to be limited to only theembodiments described herein.

While the present invention has been illustrated by a description ofvarious preferred embodiments and while these embodiments have beendescribed in some detail, it is not the intention of the Applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. The various features of the invention may beused alone or in any combination depending on the needs and preferencesof the user. This has been a description of the present invention, alongwith the preferred methods of practicing the present invention ascurrently known. However, the invention itself should only be defined bythe appended claims.

What is claimed is:
 1. A method of operating a rotor of a blood pump,comprising: levitating the rotor within a tubular body along an axis ofthe blood pump using a first magnetic bearing; rotating the rotor aboutthe axis within the tubular body using a second magnetic bearing;sensing a radial position of the rotor; and maintaining the radialposition of the rotor relative to the axis using a third magneticbearing.
 2. The method of claim 1, wherein: the first magnetic bearingcomprises first and second permanent magnets; the second magneticbearing comprises a plurality of electromagnetic coils and a polestructure coupled to the rotor; the third magnetic bearing comprises theplurality of electromagnetic coils and the first permanent magnet; andsending a current to at least one of the coils of the second magneticbearing in response to the sensed radial position in order to change ormaintain the radial position.
 3. The method of claim 1, wherein: thesecond magnetic bearing further comprises a plurality of electromagneticcoils and a pole structure coupled to the rotor; and the sensing stepfurther comprises sending a current to the plurality of electromagneticcoils, thereby magnetizing the coils.
 4. The method of claim 1, whereinat least one PID controller performs the sensing step.
 5. The method ofclaim 1, wherein at least one Hall effect sensor performs the sensingstep.
 6. The method of claim 1, further comprising: using a controllerto send a current to the second magnetic bearing in response to thesensed radial position to change or maintain the radial position.
 7. Amethod of operating a rotor of a blood pump, comprising: levitating therotor within a tubular body of the blood pump using a first magneticbearing, the first magnetic bearing comprising a first permanent magnetand a second permanent magnet, the second permanent magnet operativelycoupled with the rotor; commencing rotation of the rotor within thetubular body using a second magnetic bearing, the second magneticbearing further comprising: a plurality of vertically arranged pairs ofcoils circumferentially disposed around the housing and the firstpermanent magnet; and a pole structure coupled to the rotor; sensing aradial position of the rotor; and in response to the sensed radialposition of the rotor deviating from a threshold position relative tothe axis, sending a current to at least one of the pair of coils,thereby urging the rotor towards the axis.
 8. The method of claim 7,wherein the sensing step is performed using a plurality of Hall Effectsensors communicating with a magnetic field of the pole structure. 9.The method of claim 7, wherein the pole structure further comprises aplurality of permanent sub-magnets circumferentially disposed about acenter axis of the rotor.
 10. The method of claim 9, wherein the sensingstep further includes using a plurality of Hall Effect sensorscommunicating with a magnetic field of the plurality of sub-magnets todetect the position of the sub-magnets relative to the coils.
 11. Themethod of claim 10, wherein the current sent to each coil is equal. 12.The method of claim 7, wherein the current is sent to at least a portionof the pairs of coils after sensing that the position of a portion ofthe pole structure has rotated past at least one pair of coils, therebymagnetizing the pair of coils in a same pole direction as a poledirection in which the portion of the pole structure facing the coilsare magnetized, thereby repelling the pole structure from the magnetizedcoils in a direction, thereby rotating the rotor in the direction. 13.The method of claim 7, wherein sending the current to the pair of coils:urges the rotor towards the coils when the coils are magnetized by thecurrent in a pole direction opposite of the pole direction of the polestructure; and urges the rotor away from the pair when the coils aremagnetized by the current in a pole direction identical to the poledirection of the pole structure.
 14. The method of claim 7, furthercomprising: when the radial position of the rotor deviates from athreshold position about the axis, sending a first current to a firstpair of coils and a second current to a second pair of coilsdiametrically opposed to the first pair, the second current beinggreater than the first current, thereby urging the rotor towards theaxis and the second coil, along a path between the first and secondpairs.